Engines may utilize turbocharging to increase power density and/or increase engine fuel efficiency. However, during transient conditions, such as a driver request for increased engine output, turbocharger inertia and flow dynamics may result in “turbo lag.” Such lag may be reduced in some examples by reducing turbocharger size and weight, and/or taking various measures via engine control.
One control approach to address turbo lag uses a late fuel injection into lean diesel combustion to generate exhaust heat, thereby maintaining spin-up of the turbine of the turbocharger. Specifically, the late injection generates exhaust heat, which in turn increases the speed of the turbine. Then, when a transient occurs, such as a request for an increase in engine output, the turbine is already spinning fast enough to provide the rapid increase in engine output.
However, the inventors herein have recognized some issues with the above approach. In particular, in gasoline applications, the excess fuel used to generate increased exhaust heat may degrade fuel efficiency. For example, extended idle conditions may exist where it is unnecessary to maintain the system in a “ready” state throughout the entire operation.
The above issues may be at least partially addressed by a method for controlling engine operation for an engine having a turbocharger and direction injection in a vehicle driven by a driver, the method comprising: in response to a driver input, performing at least a first and second injection during a cylinder cycle, the first injection generating a lean combustion and the second injection injected after combustion such that it exits the cylinder unburned into the exhaust upstream of a turbine of the turbocharger, the performing of the first and second injection further responsive to turbocharger speed.
In this way, the turbocharger speed may be selectively maintained responsive to the driver's actions, which can indicate a likely intent to tip-in, for example, where turbo lag should be reduced. As another example, it may be possible to reduce fuel used to maintain turbocharger speed under selected deceleration condition, while still providing a desired fast tip-in response.